A square wave drive, a sinusoidal wave drive, a vector control and so on are known as motor drive systems. Among them, the vector control resolves a coil current of a motor into a d-axis component and a q-axis component, which are orthogonal to each other and are individually controlled. The vector control may be said to be one type of the sinusoidal wave drive. The vector control is complicated although it has an advantage of high control efficiency.
The square wave drive and the sinusoidal wave drive can be realized only with hardware such as an analog circuit or a digital circuit. On the other hand, in case of the vector control, since it is difficult to construct a control circuit only with hardware due to its complexity of the vector control, it generally relies on a software control by a combination of a processor (microcomputer) and a program.
In order to properly drive a motor, information on a mechanical state (a rotational speed and a rotor position) of the motor is required. The mechanical state of the motor can be detected by a rotation sensor such as a rotary encoder or a resolver. Alternatively, in a sensorless system, it is necessary to estimate the mechanical state of the motor based on an electrical state (a coil current and/or a coil voltage of the motor) of the motor and generate a drive control signal based on the estimated state.
FIG. 1 is a block diagram of a motor driver 4R which uses a software control. Here, sensorless drive is taken as an example. A motor 2 is a three-phase brushless motor. The motor driver 4R mainly includes a three-phase inverter 6 and a motor control circuit 10R.
The motor control circuit 10R mainly includes an A/D converter module 12, a processor 14 and a pulse width modulator 16. The A/D converter module 12 converts an analog detection signal S1 corresponding to the electrical state of the motor 2, in other words, a coil current or a coil voltage of the motor 2, into a digital detection signal S2. For example, the inverter 6 is provided with sense resistors RsU, RsV and RsW for detecting currents of U phase, V phase and W phase (which is referred to as a three-shunt configuration). In each sense resistor Rs, a voltage drop proportional to the coil current of the corresponding phase occurs. The voltage drops of the sense resistors RsU to RsW are input to the A/D converter module 12 via a plurality of analog ports. In addition, other analog signals (not shown) may be input to the A/D converter module 12.
Based on the digital detection signal S2 from the A/D converter module 12, the processor 14 generates a drive control signal (for example, a command value of a three-phase voltage) S3 of the motor 2. The processor 14 is configured to execute a program 18 described by a user in advance.
The pulse width modulator 16 generates a control signal S4 of the inverter 6 by performing a pulse width modulation (PWM) of the drive control signal S3. The inverter 6 is switched according to the control signal S4 from the pulse width modulator 16.
A function required of the motor control circuit 10R varies depending on a type of the motor 2 to be combined, a drive type of the motor 2 to be combined and an application of the motor 2 to be combined. For example, in addition to the three-shunt configuration shown in FIG. 1, there is a one-shunt configuration in which one sense resistor is shared by three phases, as a current detection system. The A/D converter processes three current detection signals in the three-shunt configuration and processes one current detection signal in the one-shunt configuration. Further, those two configurations are different from each other in terms of a proper timing of the A/D conversion.
If the motor control circuit 10R may have various applications, drive formats, and versatility and flexibility with which it may be used in combination with a motor, the number of types of products may be reduced, which is advantageous for vendors of the motor control circuit 10R from the viewpoint of a development cost and an inventory management. Further, even for purchasers (users) of the motor control circuit 10R, if it is possible to cope with various applications, driving formats and motors by using a common hardware (that is, the motor control circuit 10R) and modifying a software (that is, the program 18), a development period of various devices 1 equipped with the motor 2 may be shortened.
The present inventors have studied the motor control circuit 10R in the related art and have recognized the following problems. In other words, in the motor control circuit 10R, an order and a timing of the A/D conversion by the A/D converter module 12 and the analog ports to be subjected to the A/D conversion cannot be set and controlled by software freely, which is one of obstacles to increase the versatility and the flexibility of the motor control circuit 10R.